Display screen or portion thereof with pop-up window of graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a pop-up window of graphical user interface showing the new design; and,

FIG. 2 is a detail view thereof, shown separately for ease of illustration.

The broken line showings of the display screen, or a portion thereof, and of selected elements of the graphical user interface are for environmental purposes only and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with pop-up window of graphical user interface, as shown and described. 